A manatee swims in the Chassahowitzka, where Swiftmud says pumping can cut another 11 percent of the flow before causing any “significant harm.” Environmentalists say pumping has led to increased salinity and ruined habitat.

The folks who live along the Chassahowitzka and Homosassa rivers have noticed a lot of changes lately. Saltwater fish swimming in what used to be mostly freshwater, as freshwater fish disappear. Trees on the riverbanks toppling over, killed by an increase in salt. Barnacles growing where they never did before.

To them, the cause seems obvious: pumping too much freshwater out of the underground aquifer so people can keep their St. Augustine grass green. Overpumping cuts the flow of freshwater from the local springs into the rivers, allowing salty water from the Gulf of Mexico to begin pushing upstream.

So they were outraged when they found out the Southwest Florida Water Management District may let pumping cut back the rivers' flow even more. According to the agency commonly known as Swiftmud, the Homosassa's flow can be cut by another 5 percent and the Chassahowitzka by 11 percent before causing any "significant harm" to the environment.

"Our position is that you shouldn't take anything away from these rivers," said Brad W. Rimbey, an engineer who has lived near the Chassahowitzka for five years.

The clash turns on an unusual argument. Swiftmud's experts say the increased saltiness of the rivers is not due to overpumping. They contend it's due to climate change. That means it's not a sufficient reason to block more pumping.

"The increased salinity that has occurred is partly the result of sea level rise, and partly due to recent drought conditions that caused the flow to decline," said Marty Kelly, who is in charge of the river flow project for Swiftmud.

Still, he said, Swiftmud is now trying to run computer models to add in calculations for the continuing impact of sea level rise over the next 20 years. Those figures may eventually lead to changes in how much reduced flow Swiftmud believes the Chassahowitzka and Homosassa can stand.

Among the critics of Swiftmud's position is its former executive director, Emilio "Sonny" Vergara, who was in charge from 1997 to 2003. Cutting the two Citrus County rivers' flow "doesn't make a lot of sense," he said, "but it does allow you to withdraw a lot more water."

Swiftmud and the other four water districts are setting what are called "minimum flows and levels" for Florida's major waterways. The idea is to figure out how much more those rivers, springs and lakes can be drained for water supply purposes before causing environmental problems.

In some instances — along Central Florida's upper Peace River, for instance — that point has already been passed. Swiftmud is now trying to turn a lake near Bartow into a reservoir to hold extra water that can be dumped into the river the next time it threatens to dry up.

Swiftmud's proposed levels for the Chassahowitzka and Homosassa rivers have made residents skeptical about the whole minimum-flow program. In a recent newsletter, Ron Miller, vice president of the Homosassa River Alliance, labeled it "a statewide project to create a map of water sources available for development" that will "lead to the destruction of our already impacted springs, rivers and lakes."

Kelly said that's the opposite of what's intended. Swiftmud's experts ran computer models to check how various levels of pumping would affect the rivers as habitat for manatees, fish, birds and other flora and fauna.

Ultimately, they concluded that a 15 percent reduction in the wildlife habitat would constitute the vaguely defined standard of "significant harm." Then they calculated how much water could be taken out without hitting that 15 percent mark.

"We're protecting 85 percent of the habitat," Kelly said.

Vergara called Swiftmud's computer modeling "iffy" and questioned the experts' ability to measure the flow of tidally influenced, spring-fed rivers so accurately as to avoid hitting the "significant harm" point.

"Holy smokes, that's an awful fine point to make," he said. "And if they set that point wrong, it's going be wrong in perpetuity."

Kelly conceded that the law on setting minimum flows doesn't provide for any guard against gradual damage from increased pumping: "You're either significantly harmed or you're not."

Public workshops on Swiftmud's proposal have turned out to be "pretty feisty," said Rimbey, a forensic engineer who is with the Chassahowitzka River Restoration Committee. The next one, slated for October, promises to be no love-in. Rimbey said he's got a springs expert lined up to testify against the proposed flow levels, and he's trying to get a climatologist who will testify that there are likely to be more and longer droughts.

As far as he's concerned, Swiftmud "should be thinking about everybody having brown lawns in the Chassahowitzka springs shed before you desecrate this river."